Crystalline thermoplastics such as aromatic polyesters are well known in the art, and are in widespread commercial use, principally in the form of PBT, PPT and PET.
Polymer-polymer blends of the prior art often comprise soft or elastomeric materials with a matrix resin to provide improved toughness. Sometimes this improved toughness is manifested by an increase in resistance to a notched impact, sometimes by an improvement in elongation or falling weight impact, and sometimes by an increased ability for the molded article to be bent without breaking. In order for the soft elastomeric material to toughen the polymer matrix, it must first be dispersed well and into small particles. The small particles must be maintained as small and discrete particles during any subsequent melt processing, such as injection molding. Finally, there must be sufficient adhesion in the solid state to allow energy from an impact or otherwise distorting event to cross the interface from the matrix to the elastomeric particles for them to toughen the part.
“Compatibility” is an old and broadly used term in polymer blend technology. The meaning of compatibility is often defined by the context in which it is used. Hence, compatibility can vary in meaning from compatible to the naked eye to chemically compatible in that one ingredient will not degrade the other such as could be the case with aromatic polyesters and primary amines for example, to being present in a blend at a high level without giving a delaminated injection molded article, to being miscible at the molecular level. For purposes of this application, the term “better or improved compatibility” is defined in the Definitions section of the Detailed Description.
Manufacturers and customers of aromatic polyester compositions and the articles made from these compositions are interested in lower cost and/or improved toughness associated therewith. Thus, it is desirable to provide aromatic polyester compositions (e.g. polymer blends) such as PBT, PPT and PET and articles with improved compatibility with economical polar olefins or using less of relatively expensive elastomers such as thermoplastic polyurethanes (TPUs) or polyether polyester thermoplastics.
The following disclosures may be relevant to various aspects of the present invention and may be briefly summarized as follows:
U.S. Pat. No. 4,753,980 to Deyrup discloses toughened thermoplastic polyester molding compositions characterized by extraordinary toughness comprising 60-97 weight % of a polyester matrix resin and 3-40 weight % of an ethylene copolymer such as ethylene/methylacrylate/glycidyl methacrylate.
U.S. Pat. No. 5,641,824 to Forschirm discloses a self-lubricating polymeric composition, characterized as a melt blend of a thermoplastic polymer and a lubricating system containing ultra high molecular weight polyethylenes, a polyester, acid metal salts, calcium salts, antioxidants and stabilizers. The composition may be prepared into shaped articles, which exhibit improved surface wear resistance and coefficients of friction.